1. Field of the Invention
The present invention relates to a center-of-gravity-position lateral acceleration acquisition apparatus for acquiring lateral acceleration of a vehicle at the center of gravity of the vehicle through correction of lateral acceleration detected by a lateral acceleration sensor installed at a position remote from the center of gravity of the vehicle. The present invention also relates to a motion control apparatus for a vehicle which utilizes the center-of-gravity-position lateral acceleration acquisition apparatus.
2. Description of the Related Art
In general, in order to acquire a status of turning motion (turning behavior) of a vehicle, the lateral acceleration at the center of gravity of the vehicle and the yaw rate of the vehicle must be acquired. Since a detected value of the yaw rate of the vehicle is affected by the location on the vehicle body where the detection is performed, a yaw rate sensor for detecting the yaw rate of the vehicle need not be installed at (or in the vicinity of) the center of gravity of the vehicle.
On the contrary, a detected value of the lateral acceleration of the vehicle is affected by the location on the vehicular body where the detection is performed, because the vehicle in turning motion causes a rotational motion about its center of gravity (so-called spinning motion) in addition to an orbital motion. Therefore, if a lateral acceleration sensor for detecting the lateral acceleration of the vehicle is installed at a position remote from the center of the gravity of the vehicle, the lateral acceleration detected by the lateral acceleration sensor deviates from the lateral acceleration at the center of gravity of the vehicle by the amount corresponding to the above-described rotational motion. In other words, the lateral acceleration sensor must be installed at (or in the vicinity of) the center of gravity so as to directly detect the lateral acceleration at the center of gravity of the vehicle.
Recently, a technique has been developed for incorporating driving dynamics sensors, such as a yaw rate sensor and a lateral acceleration sensor, into a unit (hereinafter referred to as “an integrated unit”) in which a hydraulic unit (HU) including a plurality of hydraulic devices, such as a plurality of solenoid valves and hydraulic pumps, necessary for hydraulic braking force control, is integrated with an electronic control apparatus (ECU) which controls the plurality of hydraulic devices (see, for example, Japanese Kohyo (PCT) Patent Publication No. 2004-506572). In general, such an integrated unit is often installed at a position remote from the center of gravity of the vehicle (for example, in an engine room). In this case, the lateral acceleration sensor is installed at a position remote from the center of gravity of the vehicle.
As described above, in order to acquire the lateral acceleration at the center of gravity of the vehicle in the case where the lateral acceleration sensor is installed at a position remote from the center of gravity of the vehicle, the lateral acceleration detected by the lateral acceleration sensor must be corrected by an “amount corresponding to the rotational motion” of the vehicle described above. It is widely known that “the amount corresponding to the rotational motion” can be represented by the deviation (a distance in the front-back direction of the vehicle body and a distance in the lateral direction of the vehicle body) of the lateral acceleration sensor from the center of gravity of the vehicle and the yaw rate of the vehicle (and a time-differentiated value of the yaw rate).
Accordingly, the lateral acceleration at the center of gravity of the vehicle (hereinafter refereed to “corrected center-of-gravity-position lateral acceleration”) can be determined through correction of the detected lateral acceleration using the yaw rate detected by the yaw rate sensor. In this case, the yaw rate sensor must operate normally so as to obtain the corrected center-of-gravity-position lateral acceleration with high accuracy.
That is, in the case where an anomaly occurs with the yaw rate sensor and the detected yaw rate deviates from an appropriate value, the corrected center-of-gravity-position lateral acceleration cannot be acquired with high accuracy. In view of the above, it is desired to acquire the corrected center-of-gravity-position lateral acceleration through correction of the detected lateral acceleration without using the yaw rate detected by the yaw rate sensor.
Further, the following problem arises when the corrected center-of-gravity-position lateral acceleration is acquired by making use of the yaw rate detected by the yaw rate sensor. Here, a case is considered in which vehicle stabilization control for stabilizing motion of the vehicle (for example, over-steer/under-steer suppression control) is performed, and for example, a yaw rate deviation, which is a motion state quantity of the vehicle necessary for the above-described control, is obtained. Herein, the yaw rate deviation refers to a deviation between an actual yaw rate and a yaw rate (target yaw rate) determined from a speed of the vehicle and a steered angle of steerable wheels.
In addition, a case is considered in which, in order to prevent erroneous operation of the vehicle stabilization control due to occurrence of anomaly of the yaw rate sensor (that is, to provide redundancy to the control in order to cope with the anomaly of the yaw rate sensor), a first yaw rate deviation determined through direct use of the yaw rate detected by the yaw rate sensor and a second yaw rate deviation determined without direct use of the detected yaw rate are obtained, and both the yaw rate deviations are used for the vehicle stabilization control.
The first yaw rate deviation can be determined by directly using the detected yaw rate as the “actual yaw rate.” The second yaw rate deviation can be determined by using, as the “actual yaw rate,” a yaw rate estimated from the above-described corrected center-of-gravity-position lateral acceleration determined through correction of the lateral acceleration detected by the lateral acceleration sensor.
However, as described above, if the yaw rate detected by the yaw rate sensor is used in acquiring the corrected center-of-gravity-position lateral acceleration, the second yaw rate deviation will also be a value determined by indirectly using the detected yaw rate. In other words, as well as the first yaw rate deviation, the second yaw rate deviation may also be affected by the yaw rate detected by the yaw rate sensor.
Accordingly, in this case, it becomes impossible to provide redundancy to the control so as to cope with anomaly of the yaw rate sensor. From this viewpoint as well, it is desired to obtain the corrected center-of-gravity-position lateral acceleration through correction of the detected lateral acceleration without using the yaw rate detected by the yaw rate sensor.